Hi to all,
I am new on the lists but using nut on megatec for last two and half years.
Looking at archives I saw that there is a lot of people confused about battery
voltage and I want to help them to clear out some stuff in their heads.
This story is based on my experience with UPS devices from 600VA to 20kVA, from
single phase systems to three phase systems, with battery packs from 1 battery
to 62 batteries in both technologies interactive (aka stand-by) and on-line (aka
double-conversion) but all of them were "speaking" megatec. Anyway
this does not necessarily relater only to megatec enabled UPSs this is story for
all UPSs and their batteries.
On one hand we have UPS manufactures which use their own or OEM boards which are
the hart of UPS. These electronics have their battery banks which enables them
to work when mains (ups power supply) is out of specified value. Battery bank
size varies from ups to ups depending on UPS technology and back up time. How
ups electronics sees battery bank is what you get over megatec driver and this
is what I am writing about.
Battery in UPS is in 99% of cases electro-chemical product made of Pb, Sulphric
Acid, Water and some other chemical stuff to give better performance. It's
sealed, non-spill able in order to make it safer for manipulation and what is
most important its standardized by its physical and electrical characteristics.
Battery is usually made out of three or six cells in one standardized package -
this is what you know as one battery. This packed battery has two very important
electrical characteristics for your UPS: nominal voltage (V) and capacity (Ah).
Usually you will meet 6V (3 cell) and 12 V (6 cell) batteries in UPS. This
represents nominal voltage of battery.
In 70% of ups devices usually is used battery of 12V/7Ah in some rare cases
12V/9Ah or 6V/4.5Ah.
Depending on ups power rating in output different number of batteries is used
and common values are:
UPS Technology UPS rated power number
of batteries total battery voltage
Interactive 600VA 1
(12V) 12V
Interactive 1000VA 2
(12V) 24V
Interactive 2000VA 4
(12V) 48V
On-Line 1000VA 3
(12V) 36V
On-Line 2000VA 6
(12V) 72V
On-Line 3000VA 8
(12V) 96V
On-Line 5000VA 20
(12V) 240V
Since battery is electro-chemical element it doesn't have constantly rated
voltage. It's voltage is somehow in relation with its charged capacity and
this is usually identified by battery manufacturer but normally you can have
following values:
per cell
6 cell
charged state
1,60 V
9,60 V
permanently destroyed
1,70 V
10,20 V
Empty
1,80 V
10,80 V
1,90 V
11,40 V
bat low start
2,00 V
12,00 V
> 50% charged
2,10 V
12,60 V
2,20 V
13,20 V
2,30 V
13,80 V
Fully charged
Just for info, charging and discharging of batteries are not linear functions in
voltage vs. time.
When your UPS tells you battery voltage over megatec driver he tells you
actually charged value of its battery bank. This information can be told in two
ways: as a voltage sum of whole bank or as average value per battery cell. In
first case you may get 38.6V in a second case 2.14V for the same on-line 1kVA
UPS. This depend on how manufacturer implemented it.
This gets me to megatec driver and how it see battery voltage. I think that this
is job for someone to improve megatec driver in order to look at some table to
see battery charged value or to create it with parameters to driver.
Since I think I am becoming boring if you are interested how to determine charge
level I can continue writing... but this involves real time clock inside of
driver, some counters... lots of work for someone.
All best,
?eljko Barali?
Pakom Computers doo
SST Service Center Nis
Serbia
zeljko.baralic at pakom.com
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